Process of obtaining pure tin from crude tin or tin alloys electrolytically.



ing in tin alloys being subjected to electroly- To all whom it may concern:

hydrochloric acid.

OTTO STEINER, OF OBEFELD, GERMANY.

PROCESS OF OBTAINING PURE TIN FROM CRUDE TIN OR TIN ALLOYS ELECTROLYTICALLY Specification of Letters Patent.

Patented June 9, 1908.

Application filed August 10, 1907. Serial No. 388,036.

Be it known that I, Orro STEINER, subject of the Austrian Emperor, residing at Crefeld, Germany, have invented new and useful Improvements in Methods or Processes of Obtaining PureTT-in from Crude Tin or Tin Alloys Electrolytically, of which the following is a specification.

The present invention relates to a method of refining tin electrolytically, particularly for extracting pure tin from alloys, wastages, residues etc. with the extraction of the foreign metals.

In the English patent specification No. 297 of the year 1895 (Claus), a method for relining tin electrolytically is described, consistsis in an alkaline sulfur solution at a temrferature of 90 C. and a current density of 1 ampere per square decirneter of electrode surface. Pure tin is precipitated at thecathode, whereas the impurities are deposited as sulfids and collect at the bottom of the bath. If, however, antimony and arsenic are contained in the tin alleys which is employed as anode, these are deposited together with the tin at the cathode. If the tin is to be freed from these admixtures, the cathode deposit must be subjected to electrolysis a second time in a solution of sodium thio-sulfato in In the practical execution of the method according to the present invention it has been found that is is possible in an alkaline sulfur solution to obtain a compact metallic deposit of pure tin at the cathode in one single operation when the necessary precautions are observed.

Firstly, plates of pure tin or tin-)lated plates or sheets are employed as cathodes. On other metals, as iron, copper etc, the tin precipitated spongy with generation of gas.

Secondly, care must be taken that the tension between the anode and cathode amounts to less than 0.2 volt. 1f the tension between the electrodes exceeds this amount, a sudden rise of tension up to 0.6 volt and violent generation of gas or decomposition of the electrolyte takes place. That fact is caused by sudden and violent evolution of hydrogen gas. See also the journal Electrochemical page 309.

and i'lletallu'rg icdl Industry 1907, The previously metallic-bright cathode deposit becomes dull, sponge-like and oxidizes.

As the electrode tension is dependent on the current density, of the concentration of the lye and of the distance between the electrodes, the tension may easily be l iept below the critical limit of 0.2 volt by varying these components. When employing a 10 of sodium solution as electrolyte and a distance between the electrodes of 17; cm., current strengths up to 2' ampere per square decimeter of electrode surface can be employed without the tension reaching the amount of 0.2 volt. If the proportion of sulfidof sodium in the electrolyte is in creased, correspondingly higher strengths of current can be employed which is of great importance commercially, for by raising the current density, the capacity of reduction of the apparatus is increased, {11M the duration of the electrolysis is shortened In this manner the loss of tin from the tin which is employed in the plant, as well as the general costs, is considerably diminished.

Further, before suspending fresh tin an-- odes having a brightinetallic surface in the electrolyte, about 1 of the weight of the electrolyte of sulfur must bcdissolved in the same. This sulfur is preferably employed in the form of flowers of sulfur. it becomes precipitated as sul'lid at the surface of the anodes and, acting thus depolarizcr, it enables the electrolysis to commence with low tension. If the addition of sulfur is omitted before suspending new crude tin anode behaves as an insoluble anode, and after closing the circuit the tension rises at once to 0.6 volt, violent generation of gas and decomposition of the electrolyte takes place, but no tin is deposited. The cathodes become dull, and are then no longer usable for the further deposition of tin. The same electrolyte may be employed repeatedly for electrolysis if sulfur is again added to the bath before suspending fresh anodes. The electrolyte can thus be kept for months in a condition fit for use.

Further, the electrolysis is to be carried out so that the anode mud which is on the bottom of the bath and that which is at tached to the anodes is not disturbed. In order to attain this all the operations must be carried out so that no violent movements occur in the electrolyte. In this method, therefore, the lye cannot be circulated as in the electrolytic refining of copper. lt, 1s

iatcd indirectly by steam iif preferably l each bath. by itself and at the bottom 0.

sul'lid P anodes, the

.each batliawhereby-the lye is prevented at upontheelectrodes, together with the,anode the current is.-

- tus, one cathode iron, or wood process the electrolyte is allowed to flow away veryislowly through an overflow pipe Lastl- I generall 1 low tension of much importance for the con'ducti n of the section through theapparatus,

of the apparatus,

' the anodesf b are the cathodes which are likewise con? nected with the conductor 6 by'meanso'ftin' stri s e, tin buttonsd",and copper'barsc, an they rest ori insulating barsg onthe op posits side. Theseanodes fand cathodes'l'i are suspended alternately in the"cellS.j. ;The conten't and size of t e cells depend onthe circumstances of each case. As already mentioned, I the- 'thickness, of the anodes the sametime from being decomposed by theelectrolysis. .After each electrolytic where-' placediabdve the bottom of the bath mu arethen removed and new electrodes suspended; the clear electrolyte 'is then allowed toilow'in, 1 7/ sulfurand so muchsulfid of sodium aregaddedjthat the original percenta e of sulfid of sodium is. produced again, and e ectrolysis iscommenced again. 1

care mustbetaken here also,-'as is assmall as possiblef usual, thatth electrode-contacts '5' is a cover for closin the'electriccell; of all the electrodes in a batlrzare made as j ,kjis asteamcoil used forhealtingthe elecgood anduniform as possible. l-As'only very ;trolyt e. v

0.1 to,0.'18-vo ltfcan bewcrked lis a -siphonforletting ofi theclearlye, With in this method, small resistances are of ;and m an opening which is used for drawm'g oil the mud and which can be closed by a plug or the like.

l m'; the thickness of the cathodes should be current,- with poon-orjnon-umforrn contacts distributedxver unequally to;.' I the individual electrodes of t ebathwhich, arranged in place of the siphon Z. Inthis besides-the; disadvantage of )working' unj'f case it is arranged that the ta p is placed equally, also causes; very different tensions through a socket 0, and it can e opened or between the 'individ ual anodes andcathodes closed-by turning the key g. Instead of the of a -bath, so that in many electrolytes only siphon or tap similar optional suitable means gas is generated, inothers tin isdeposited, can of course be employed.

amounts at the commencement to ahoutljto and in others nothing takes. place at all, The mode of operation with such or simi- Very uniform electrode contacts can be ob.- lar a paratus is as follows: As anode mate-. tained inaiquick and simple manner by solrial l eruvian or Bolivian tin is employed of dering the eectrodes direcbtly tothe'homogeabout the following composition: neous'tinne conductin ars. I T

The illustrations Fig dies 1 to 5 on the 830-" i f bg 3 2 companying drawing represent apparatus as mlony t 0 5 n is used for carrying the method in accordf H ance with the present invention into pr'acclsmu U 1; 0 1 tice. It isof course understood that these f," H illustrations only represent one particular form ofsuch apparatus, andv that in practice 1 Y f all similar suitable apparatus can be Sem- Traces of gold, sulfur,.oxygen, etc.

As already mentioned, plate-shaped anodes are cast of this composition about 1 to 1% cm. thick as in the electrolytic refining of copper, whereas the cathodes consist of very thin sheets of pure tin. The temperature of the electrolyte is main With a current of 0. meter. of electrode ployed if only they are similar in principle to the apparatus described hereafter.

1n the drawing :Fig. 1 is a vertical crossone anode plate being seen .in elevation; Fig. 2 shows a vertical. cross-section through the ap ara hate being seen in e evation; Fig. 3 is ,a longitudinal vertical section through the apparatus; Fig. 4 is a plan :tlle cover having been removed, and Fig. 5 is a longitudinal vertical section through one end of the,apparatus in a somewhat modified form. Referring tdthe figures, a is the box which is made of any optional suitable material, as coated with lead, or the. like; b is the conductor-supplying current to the anodes. This conductor preferably goes first to a strip a of copper on which tin but tons d are arranged. To these tin buttons there are strips 6" of tin connected and are'soldered to the latter. 0n the other side the anodes rest on insulating bars'g.

surface, the tension. be-

short time after the circuitihasbeenclosed, the cathodesare covered with a metallic compact layer 'of quite pure' tin (99.9% tin) metals, as lead, antimony, copper, iron, bismuth, silver, gold, etc., remain behind as anode mud attaching for the most part to the anode. After about 14 days uninterrupted electrolysis, the tension rises to about 0.14 volt. Th'e electrolyte is now drawn off through the above mentioned overflow pipe, and the cathodes as well as the anode residues are removed from the bath. The cathodes may be melted down directly. The anode mud is first scraped off from the anode volt. After quite a tween' the electrodes amounts to about 0.1

tained at about 90 Of 9 ampere per square deciwhereas the other ally, the percentage ofcopper of the anode is crease the percentage of ously stated.

- which enables ure,

. se ate residues and then worked further for ob taining the lead, antimony, silver, bismuth, gold, etc. As some sulfid of sodium is always consumedby oxidation and by theior matron "of sulfostannate,it is necessary, to insulfid of sodium in the lye again to 10% before commencing the .next electrolysis most favorable results are obtained in practice; It is of course understood that the ercentagle of sulfid of sodium in the electro yte and t e current density per unit of area of electrode surface can'be varied within certain limits having regard to'what has been previ- For this the percenta e of tin in the anode material is decisive, simi arly as, for example, in refining copper electrolytico f influence in the choice of the current density at-the electrode.-

The new method hereinbefore described is at all events up to the present the only one compact and metallic deposits oftin 0 optional thickness tobe obtamed electrolytically.

What I claim as my invention and desire to secure by Letters'Patent is 1. The method of obtaining pure tinfroni mode of working.

crude tin or ti-n alloys which trolytically tion of an consists in elecdissolving the crude tin in a solutin, and maintaining an electrical tension of less than 0.2 volts between the electrodes.

2. The method of obtaining pure tin from crude tin or tinalloys which consists in electrolytically dissolving the crude tin in a solu- 7 tion of an alkali sulfid and simultaneously plating'out the tin u on a cathode of {pure tin, maintaining an e ectrical tension 0 than 0.2 volts between the electrodes, re enerating the electrolyte by adding some su ur theretovv and reusing it to ele'ctrol'yze fresh anodes.

I I 3.- The method of obtaining tin fromcrude tin or tin alloys which consists in treating the impure tin asan anode in an electrolyte com sulfid solution, deposit, 'ing the tin upon a cathode having a pure tin osed of an alkaline surface, maintaining the tension between the electrodes at less than'O' Z volts, and keeping the electrolyte quiescent inorder to avoid disturbing the mud de .o'sited in the bottom of the bath, removing she anode residues, regenerating the electrolyte b adding sulfur thereto and reusing it to .ele anodes. I

In testimony whereof I have signed my name to this specification in the-presence of two subscribing witnesses.

o'rro s'rnruna'.

Witnesses:

Hnmmcn Disnna'r'," G. Rrvonnna.

alkali sulfid and simultaneously plating out the tin upon a cathode of pure ctrolyze fresh less 

